I have installed that update on the first day (like any other update). Never had a problem with either update nor am I seeing the sustained notes cutting off. Just as a data point.

When you see unresolved reports of problems, it is not wise to make generalities about the firmware. I'm assuming you're referring to the SSS thread - I wasn't able to find anything (quickly) about general sustain other than v2.50 fixes a freeze problem when using the footswitch and sustain pedal simultaneously:

Fixed a problem in which the footswitch would freeze when it's used as a sostenuto in combination with the sustain pedal.

So this would be more of a problem prior to v2.50 and less of an issue after update if you use pedals as stated.

... AND - just to be perfectly clear:

The footswitch jack on the back of your Montage, which accepts an FC5 type simple momentary footswitch is assignable to various functions or CC numbers. Some CC numbers are generic and some will be interpreted as specific controllers within Montage. I believe the range of CC values you can set is anything between 1-95. If you set the FS input to CC 66 - then your footswitch will be interpreted as a Sustenuto switch. It should only raise the virtual hammers of notes which you are pressing the piano keys. Any notes you are not pressing (when the footswitch is activated) will not have their hammers lifted and will not sustain.

What this bug fix is stating is that if you use your FS in that manner, assigning it to CC #66 - AND used the sustain pedal (another pedal hooked up to the sustain pedal jack) then in past firmware versions this would cause your footswitch (sustenuto function) to freeze. Now that is fixed for the few who meet the bug's criteria.

If you think the rarely employed (at least in most written music) middle-pedal is interesting then experiment with using the footswitch in order to simulate sostenuto.

... AND - more "extra credit" - (to steal a phrase) - meaning - related but not necessarily tightly coupled to the original thread:

If you want to emulate 3 pedals - you can do that. The soft pedal MIDI CC is not honored in Montage - but there's a different way. To make things easier, you can hook up an FC5 to the FC2 or FC1 (foot controller 2 or 1) jacks on the back of Montage. Each has a "default" usage in Montage's Presets - so you'll need to choose which one to "kill" due to using an FC as a "binary" (just on or just off) port rather than continuous controller (for volume or superknob).

Once the FC5 (a kind of footcontroller) is plugged into the FC1 or FC2 ports - then you can modify a piano Performance to do something with the FC5 (foot controller) is pressed. You would go into the Control/Mod menu of the Performance and assign the footcontroller (1 or 2) you have the FC5 connected to as the SOURCE and volume as the DESTINATION. There are easier ways to assign - you could also highlight the volume parameter for the Performance - which should illuminate the [CONTROL ASSIGN] button, press the [CONTROL ASSIGN] button - then press the footswitch (the one you have plugged into FC1 or FC2) to set up the association. Then you'll want to set a negative offset for the right side of the curve. You can set the curve as bipolar. Pick a curve that allows the left-most side to be "0" and right-most side to be a negative value. Values in the middle do not matter since the pedal only will output 0 or 127. You can also setup a user curve if you cannot find a built-in one. However, there should be a built-in curve that suits.

After you have the negative offset of volume setup properly, you should get semi-correct response.

Even better would be the destination, instead of volume, would be velocity offset. Because this is actually what is happening in the piano (hammers moving to limit velocity). You can find the velocity offset and experiment with that as well.

Now you would have 3-pedal support for your modified piano performance (after [STORE]'ing as a user performance so you can return to the same settings).